Cooling structure of cylinder block

ABSTRACT

In a cooling structure of a cylinder block, a cooling medium is supplied into the cylinder block in which a water jacket continuously extends around a bore wall, so as to uniform the bore wall temperature. The cooling structure sets a cooling characteristic of the water jacket based on at least one of variation in the bore wall temperature in a direction perpendicular to the axis of the borehole and variation in the temperature of the cooling medium flowing around the bore wall. The structure improves the cylinder bore cooling efficiency or the cooling uniformity.

[0001] The disclosure of Japanese Patent Application Nos. 2000-197733filed on Jun. 30, 2000, 2000-209464 filed on Jul. 11, 2000 and2000-213264 filed on Jul. 13, 2000 including the specification, drawingsand abstract are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Invention

[0003] The invention relates to a cooling structure of a cylinder block.

[0004] 2. Description of Related Art

[0005] In an engine cylinder block, a water jacket is formed around acylinder bore wall. Engine-cooling water is circulated in the waterjacket to cool the cylinder bore wall heated from the combustionchambers.

[0006] In this construction, the temperature of the cylinder bore wallis unlikely to become uniform. The reason for the temperaturenon-uniformity is as follows. With respect to the circumferentialdirections relative to the cylinder bore wall, the temperature ofportions in contact with two side portions of the cylinder bores in thedirection of alignment of the cylinder bores where the flow speed isgreat is lower than the temperature of inter-cylinder bore portionswhere the flow stagnates. With respect to the up-down direction relativeto the cylinder bore walls, the temperature of upper portions of thecylinder bore walls closer to the combustion chambers is higher than thetemperature of lower portions thereof. Furthermore, with respect to thedirections of alignment of the cylinder bores, the temperature becomeshigher toward a downstream side.

[0007] The non-uniformity of cylinder bore wall temperature gives riseto various problems including degraded fuel economy, increased emissionsof unburned hydrocarbons (HC), etc. For example, if the cylinder borewall temperature varies in the circumferential direction, the shape of acylinder bore wall deviates from a circular shape, thus resulting indegraded follow-up characteristics of the piston and oil rings withrespect to the bore wall internal surface. If the ring tension isincreased in order to prevent degradation of the follow-upcharacteristics, the friction in sliding movements increases, resultingin degraded fuel economy. Furthermore, if the cylinder bore walltemperature varies in the up-down direction, the evaporation andcombustion of fuel deposited on an intermediate portion of each borewall in the updown direction deteriorates in the case of, for example, adirect fuel injection gasoline engine or the like, thus resulting indegraded fuel economy, reduced torque, and increased emission ofunburned hydrocarbons (HC).

[0008] To curb these drawbacks, a uniform cylinder bore wall temperatureis desired. Although there have been various proposals of improvementsmade regarding a water jacket of a cylinder block itself for the purposeof improving the wall temperature distribution or the like, most of themcannot be easily applied to mass production in view of productivity,mold service life, strength, etc. Some proposals have been made forimproving the cylinder bore wall temperature distribution by disposing,in the water jacket of a cylinder block, a spacer (a means foruniforming the bore wall temperature by partially filling a space of thewater jacket) formed separately from the cylinder block.

[0009] For example, Japanese Utility Model Application Laid-Open No. SHO57-43338 discloses a cylinder block in which a water jacket is formedaround a borehole, and a spacer whose shape is different from the shapeof the water jacket in the direction of a borehole axis but is identicalto the water jacket shape in the circumferential direction is disposedin the water jacket.

[0010] In this structure, a sufficient amount of cooling water issupplied around an upper portion of the borehole that is close to thecombustion chamber and therefore is exposed to high temperature, and thespacer is disposed near a lower portion of the borehole that is remotefrom the combustion chamber and therefore is not exposed to hightemperature so that supply of an unnecessary amount of cooling water iseliminated. Therefore, the structure advantageously improves the coolingwater supplying efficiency.

[0011] However, the cylinder block cooling structure described inJapanese Utility Model Application Laid-Open No. SHO 57-43338 and thelike has the following drawbacks.

[0012] (1) Although the bore wall near the cooling water inlet is cooledby low-temperature cooling water, the cooling water temperatureincreases during the passage through the surrounding of thehigh-temperature bore wall, so that the cooling of the bore wall becomesinsufficient near the cooling water outlet. Due to the different borewall cooling efficiencies in the bore wall circumferential direction,the borehole non-uniformly deforms. As a result, the bore wall follow-upcharacteristic of the piston and the like deteriorates, and the frictionincreases, and the fuel economy deteriorates.

[0013] (2) In a cylinder block having an open structure in which a waterjacket is formed continuously around a plurality of bores, inter-boreportions receive heat transferred from the adjacent bores, but are notsupplied with sufficient amounts of cooling water. Therefore, theinter-bore portions tend to have higher wall temperature than otherportions. Due to the different bore wall cooling efficiencies of theinter-bore portions and the other portions, the boreholes non-uniformlydeform.

SUMMARY OF THE INVENTION

[0014] It is an object of the invention to provide a cooling structureof a cylinder block capable of improving the cylinder block coolingefficiency and the cooling uniformity.

[0015] A cooling structure of a cylinder block in accordance with afirst mode of the invention includes a water jacket continuouslyextending around a cylinder bore wall so as to convey a cooling medium,and a mechanism that sets a cooling characteristic of the water jacketbased on at least one of a variation in a temperature of a cylinder borewall in a direction perpendicular to an axis of boreholes and avariation in a temperature of the cooling medium in the directionperpendicular to the axis of boreholes, passing around the bore wall.

[0016] The setting of the cooling characteristic of the water jacket maybe accomplished by disposing a spacer in the water jacket.

[0017] In the first mode, the cooling characteristic of the water jacketis set based on at least one of variation in the bore wall temperaturein the direction perpendicular to an axis of the cylinder borehole andvariation in the temperature of the cooling medium temperature in thedirection perpendicular to an axis of the cylinder borehol passingaround the bore wall. Therefore, the cylinder bore wall temperature canbe uniformed by enhancing the cooling at a site of high cylinder borewall temperature and weakening the cooling at a site of low cylinderbore wall temperature. Hence, non-uniform deformation of a borehole canbe reduced.

[0018] In a cooling structure of a cylinder block in accordance with asecond mode of the invention, the position of cooling around thecylinder bore is changed in accordance with the state of engine load.

[0019] According to the second mode, since the cooling position aroundthe cylinder bore is changed in accordance with the state of engineload, it is possible to prevent a lower portion of a cylinderbore-surrounding portion from having high temperature during a high-loadengine operation, by cooling the lower portion of the cylinderbore-surrounding portion during the high-load engine operation.

[0020] In a still another mode of the invention, a portion of the spacerdisposed in a cooling water inlet portion or a cooling water outletportion of the cylinder block may have a structure for reducing the flowresistance.

[0021] According to this mode, since the portion of the spacer disposedin the cooling water inlet portion or the cooling water outlet portionof the cylinder block has a structure for reducing the flow resistance,the flow resistance of inflow and outflow of the cooling water withrespect to the water jacket in the cylinder block is reduced, so thatthe drive efficiency of a water pump will improve. Furthermore, theinflow and outflow of the cooling water with respect to the water jacketbecomes smooth and stable, thus giving good effect on the coolinguniformity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The foregoing and further objects, features and advantages of thepresent invention will become apparent from the following description ofpreferred embodiments with reference to the accompanying drawings,wherein like numerals are used to represent like elements and wherein:

[0023]FIG. 1 is a plan view of a cylinder block cooling structure inaccordance with Embodiments 1 to 7 and 43 to 54 of the invention;

[0024]FIG. 2 is a sectional view of a portion of the cylinder blockcooling structure in accordance with Embodiments 1 to 7 of theinvention;

[0025]FIG. 3 is a sectional view of a thrust/counterthrust portion ofthe cylinder block cooling structure of Embodiment 1 of the invention;

[0026]FIG. 4 is a sectional view of a thrust/counterthrust portion ofthe cylinder block cooling structure of Embodiment 2 of the invention;

[0027]FIG. 5 is a sectional view of a thrust/counterthrust portion ofthe cylinder block cooling structure of Embodiment 3 of the invention,or a sectional view of an inter-bore portion of the cylinder blockcooling structure of Embodiment 4 of the invention;

[0028]FIG. 6 is a sectional view of a thrust/counterthrust portion ofthe cylinder block cooling structure of Embodiment 3 of the invention;

[0029]FIG. 7 is a sectional view of an inter-bore portion of thecylinder block cooling structure of Embodiment 4 of the invention;

[0030]FIG. 8 is a sectional view of a high-bore wall temperature portionof the cylinder block cooling structure of Embodiment 5 of theinvention;

[0031]FIG. 9 is a sectional view of a high-bore wall temperature portionof the cylinder block cooling structure of Embodiment 6 of theinvention;

[0032]FIG. 10 is a sectional view of an inter-bore portion of thecylinder block cooling structure of Embodiment 7 of the invention;

[0033]FIG. 11 is a plan view of a cylinder block cooling structure inaccordance with Embodiments 8 to 12 of the invention;

[0034]FIG. 12 is a sectional view of apportion of the cylinder blockcooling structure in accordance with Embodiments 8 to 12 of theinvention;

[0035] FIGS. 13A-13C show sectional views of the cylinder block coolingstructure of Embodiment 8 of the invention taken at a cooling waterinlet, an intermediate portion, and a cooling water outlet;

[0036]FIGS. 14A, 14B and 14C are sectional views of the cylinder blockcooling structure of Embodiment 9 of the invention taken at the coolingwater inlet and the cooling water outlet;

[0037]FIGS. 15A and 15B show sectional views of the cylinder blockcooling structure of Embodiment 10 of the invention taken at the coolingwater inlet and the cooling water outlet;

[0038]FIG. 16 is a plan view of a cylinder block cooling structure inaccordance with Embodiments 11 and 12 of the invention;

[0039]FIG. 17 is a sectional view of the cylinder block coolingstructure of Embodiment 11 of the invention;

[0040]FIG. 18 is a sectional view of the cylinder block coolingstructure of Embodiment 12 of the invention;

[0041]FIG. 19 is a sectional view of a cylinder block cooling structureof Embodiment 13 of the invention;

[0042]FIG. 20 is a sectional view of a cylinder block cooling structureof Embodiment 14 of the invention;

[0043]FIG. 21 is a sectional view of a cylinder block cooling structureof Embodiment 15 of the invention;

[0044]FIG. 22 is a sectional view of a cylinder block cooling structureof Embodiment 16 of the invention;

[0045]FIG. 23 is a sectional view of a cylinder block cooling structureof Embodiment 20 of the invention;

[0046]FIG. 24 is a perspective view of a cylinder block coolingstructure of Embodiment 22 of the invention;

[0047]FIG. 25 is a sectional view of the cylinder block coolingstructure of Embodiment 22 of the invention;

[0048]FIG. 26 is a sectional view of a cylinder block cooling structureof Embodiment 23 of the invention;

[0049]FIG. 27 is a sectional view of a cylinder block cooling structureof Embodiment 24 of the invention;

[0050]FIG. 28 is a sectional view of a cylinder block cooling structureof Embodiment 25 of the invention;

[0051]FIG. 29 is a sectional view of a cylinder block cooling structureof Embodiment 26 of the invention;

[0052]FIG. 30 is a sectional view of a cylinder block cooling structureof Embodiment 27 of the invention;

[0053]FIG. 31 is a sectional view of a cylinder block cooling structureof Embodiment 28 of the invention;

[0054]FIG. 32 is a plan view of a cylinder block cooling structure ofEmbodiment 35 of the invention;

[0055] FIGS. 33A-33E show sectional views of the cylinder block coolingstructure of Embodiment 35 of the invention taken at various sites;

[0056]FIG. 34 is a sectional view of a cylinder block cooling structureof Embodiment 38 of the invention;

[0057]FIG. 35 is a sectional view of a cylinder block cooling structureof Embodiment 43 of the invention;

[0058]FIG. 36 is a sectional view of a cylinder block cooling structureof Embodiment 44 of the invention;

[0059]FIG. 37 is a sectional view of a cylinder block cooling structureof Embodiment 45 of the invention;

[0060]FIG. 38 is a sectional view of a cylinder block cooling structureof Embodiment 46 of the invention;

[0061]FIG. 39 is a sectional view of a cylinder block cooling structureof Embodiment 47 of the invention;

[0062]FIG. 40 is a sectional view of a cylinder block cooling structureof Embodiment 48 of the invention;

[0063]FIG. 41 is a sectional view of a cylinder block cooling structureof Embodiment 49 of the invention;

[0064]FIG. 42 is a sectional view of a cylinder block cooling structureof Embodiment 50 of the invention;

[0065]FIG. 43 is a sectional view of a cylinder block cooling structureof Embodiment 51 of the invention;

[0066]FIG. 44 is a sectional view of a cylinder block cooling structureof Embodiment 52 of the invention;

[0067]FIG. 45 is a sectional view of a cylinder block cooling structureof Embodiment 53 of the invention;

[0068]FIG. 46 is a sectional view of a cylinder block cooling structureof Embodiment 54 of the invention;

[0069]FIG. 47 is a sectional view of a cooling water inlet portion andits adjacent portion of a cylinder block cooling structure of Embodiment55 of the invention;

[0070]FIG. 48 is a sectional view of a cooling water inlet portion andits adjacent portion of a cylinder block cooling structure of Embodiment56 of the invention;

[0071]FIG. 49 is a sectional view of a cooling water inlet portion andits adjacent portion of a cylinder block cooling structure of Embodiment57 of the invention;

[0072]FIG. 50 is a plan view of the cylinder block cooling structure ofEmbodiment 57.

[0073]FIG. 51 is a view taken in a direction indicated by A in FIG. 50.

[0074]FIG. 52 is a plan view of a cylinder block cooling structure inaccordance with Embodiments 58, 59 and 60;

[0075]FIG. 53 is a sectional view of the cylinder block coolingstructure of Embodiment 58 of the invention (including a section takenon line VXIII-VXIII in FIG. 52);

[0076]FIG. 54 is a sectional view of the cylinder block coolingstructure of Embodiment 59 of the invention (including a section takenon line VXIII-VXIII in FIG. 52);

[0077]FIG. 55 is a sectional view of the cylinder block coolingstructure of Embodiment 60 of the invention (including a section takenon line VXIII-VXIII in FIG. 52);

[0078]FIG. 56 is a sectional view of the cylinder block coolingstructure of Embodiment 60 of the invention;

[0079]FIG. 57 is a plan view of a cylinder block cooling structure ofEmbodiment 61 of the invention;

[0080]FIG. 58 is a sectional view of a cylinder block cooling structureof Embodiment 62 of the invention (section taken on line VXVIII-VXVIIIin FIG. 57);

[0081]FIG. 59 is a plan view of a cylinder block cooling structure ofEmbodiment 63 of the invention;

[0082]FIG. 60 is a sectional view of the cylinder block coolingstructure of Embodiment 63 of the invention (section taken on lineVIX-VIX in FIG. 59);

[0083]FIG. 61 is a sectional view of a cylinder block cooling structurein accordance with a related art;

[0084]FIG. 62 is a sectional view of a cylinder block cooling structurein accordance with a related art, and a temperature distribution diagramthereof;

[0085]FIG. 63 is a sectional view of a cooling water inlet portion andits adjacent portion of a cylinder block side portion of a cylinderblock cooling structure in accordance with a related art;

[0086]FIG. 64 is a sectional view of a cooling water inlet portion andits adjacent portion of a cylinder block cooling structure in accordancewith a related art which has a slit;

[0087]FIG. 65 is a plan view of a cylinder block cooling structure inaccordance with a related art;

[0088]FIG. 66 is a sectional view of a cylinder block cooling structurein accordance with a related art (a section taken on line VIXVI-VIXVI inFIG. 65);

[0089]FIG. 67 is a cooling water inlet portion and its adjacent portionin a cylinder bore upper portion of cylinder block cooling structure inaccordance with a related art;

[0090]FIG. 68 is a longitudinal sectional view of a cylinder blockincluding a cooling water inlet portion in a cylinder block upperportion in a cylinder block cooling structure in accordance with arelated art;

[0091]FIG. 69 is a plan view of a cylinder block cooling structure inaccordance with a related art, including a cooling structure outletportion; and

[0092]FIG. 70 is a sectional view of a cylinder block cooling structurein accordance with a related art, including a cooling water outletportion (a section taken on line VIIX-VIIX in FIG. 69).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0093] Cylinder block cooling structures in accordance with embodimentsof the invention will be described with reference to the accompanyingdrawings. In the embodiments of the invention, like component portionsare represented by like reference characters in the drawings.

[0094] A cooling structure of a cylinder block will first be describedwith reference to, for example, FIGS. 1 to 3.

[0095] A cylinder block 1 has a cooling water inlet portion 6 and acooling water outlet portion 7. Engine-cooling water from a water pumpenters a cylinder block water jacket 2 via the cooling water inletportion 6, and flows in a cylinder head water jacket, and flows out ofthe cooling water outlet portion 7. Engine-cooling water from the waterpump may directly flow into the cylinder block 1, or may first flow intoa cylinder head before flowing from the cylinder head into the cylinderblock 1. Although in the example shown in FIG. 1, two cylinders areprovided, the number of cylinders is not limited to two, but may be anynumber, for example, one, three, four, six, eight, etc. Although in theexample of FIG. 1, the cooling water inlet portion 6 is located in aside portion of the cylinder block 1, the cooling water inlet portion 6may be provided in an upper portion of the cylinder block 1.

[0096] A cylinder block structure 1 sets a cooling characteristic of thewater jacket 2 based on at least one of variation in the bore walltemperature in the direction perpendicular to an axis of boreholes 3 andvariation in the temperature of the colling medium passing around thebore wall 4. In the cylinder block structure, a spacer 5 uniforms thetemperature of the wall 4 of the cylinder bores 3 by partially filling aspace within the water jacket 2 so as to adjust the area on the cylinderbore wall 4 that cooling water contacts and the strength of impact ofcooling water on the contact area. For example, in the verticaldirection, an upper portion of the cylinder bore wall 4 tends to have ahigher temperature due to heat from the combustion chamber. Therefore,an external surface of a lower portion of the cylinder bore wall 4 iscovered with the spacer 5 so that cooling water selectively cools theupper portion of the cylinder bore wall 4 more strongly. In the cylinderbore circumferential direction, the spacer 5 causes a great amount ofcooling water to contact an inter-cylinder bore portion, and serves toincrease the flow speed. In both side portions with respect to thedirection of the cylinder bore alignment, the spacer 5 serves to reducethe flow speed.

[0097] It is desirable that the spacer 5 be formed separately from thecylinder block 1, and be disposed within the water jacket 2 of thecylinder block 1. The reason for this preference is that the separateprovision of the spacer 5 increases the degree of freedom in the moldconstruction in the casing of the cylinder block, and increases theproductivity, and eliminates the adverse effect that the deformation ofthe cylinder block external walls caused at the time of joining thecylinder head has on the cylinder bore, and the like. However, it isalso practicable to form the spacer 5 together with the cylinder block1. The material of the spacer 5 is arbitrary, for example, a metal, aresin, a rubber, a sponge, etc. It is desirable that the material be amaterial that allows the spacer 5 to deform upon receiving externalforce and to absorb the force, in order to keep the cylinder bore freefrom the adverse effect of deformation of an external wall of thecylinder block when the cylinder block is firmly bolted with thecylinder head.

[0098] Constructions in accordance with Embodiments 1 to 7 of theinvention in which the spacer 5 is formed separately from the cylinderblock 1, and is disposed within the water jacket 2 will be describedwith reference to FIGS. 1 to 10. In each construction, the spacer 5serves to uniform the bore wall temperature in the cylinder borecircumferential direction.

[0099] More specifically, in Embodiments 1 to 7, the spacer 5 has atleast one of the structures in accordance with Embodiments 1 to 7.

[0100] Embodiment 1 (FIGS. 1, 2 and 3):

[0101] The cooling water-contact area of the outer peripheral surface ofthe cylinder bore wall is made smaller on thrust/counterthrust sides 2 bthan on an inter-bore portion 2 a. FIG. 2 shows a section of theinter-bore portion 2 a taken on line II-II in FIG. 1. FIG. 3 shows asection of a thrust/counterthrust side 2 b taken on line III-III inFIG. 1. In order to avoid increases in the flow passage resistance, thepassage sectional area is set substantially constant. That is, thepassage sectional area A cm2 indicated in FIG. 2 is equal to orapproximately equal to the passage sectional area B cm2 indicated inFIG. 3.

[0102] Embodiment 2 (FIGS. 1, 2 and 4):

[0103] The cooling water passage is made narrower on thethrust/counterthrust sides 2 b than on the side of the inter-boreportion 2 a. FIG. 2 shows a section of the inter-bore portion 2 a. FIG.4 shows a section of a thrust/counterthrust side 2 b.

[0104] Embodiment 3 (FIGS. 1, 2, 5 and 6):

[0105] The heat transfer rate of the spacer 5 is made lower on thethrust/counterthrust sides 2 b than at other sites, based on material orstructure. FIG. 2 shows a section of the inter-bore portion 2 acorresponding to one of the other sites. FIG. 5 shows a section of athrust/counterthrust side 2 b. An example in which the heat transferrate is reduced based on material is shown in FIG. 5. In FIG. 5, thematerial of the spacer 5 is, for example, a rubber or an open cell foamrubber. Low-heat transfer rate portions 5 a of the spacer 5 are made of,for example, an isolated cell foam rubber. An example in which the heattransfer rate is reduced based on structure is shown in FIG. 6. In FIG.6, an air layer 5 c or an oil layer is formed in the spacer 5.

[0106] Embodiment 4 (FIGS. 1, 2, 5 and 7):

[0107] The heat transfer rate of the spacer 5 is made higher on the sideof the inter-bore portion 2 a than at the other sites, based on materialor structure. FIG. 2 shows a section of a thrust/counterthrust side 2 b.FIG. 5 shows a section of the inter-bore portion 2 a. An example inwhich the heat transfer rate is increased based on material is shown inFIG. 5. In FIG. 5, the material of the spacer 5 is a rubber or an opencell foam rubber, and high-heat transfer rate portions 5 b of the spacer5 are made of, for example, a metal or a resin. An example in which theheat transfer rate is increased based on structure is shown in FIG. 7.In FIG. 7, a lower portion of the water jacket is filled with a spacer 5made of a high-heat conductivity material, so that heat is transferredfrom the cylinder bore wall to the cylinder block outer wall by heatconduction, and is dissipated from the outer wall.

[0108] Embodiment 5 (FIG. 1, 2 and 8):

[0109] At a cylinder bore portion with a higher wall temperature thanother portions (FIG. 2), for example, at an inter-bore portion (FIG. 8),the spacer 5 has a slit 5 d that forms a gap between the spacer 5 andthe outer peripheral surface of the cylinder bore wall 4. Cooling wateris passed through the slit 5 d to cool the cylinder bore wall 4.

[0110] Embodiment 6 (FIGS. 1, 2 and 9):

[0111] In a cylinder bore portion (FIG. 9) with a higher walltemperature than other portions (FIG. 2), a taper portion 5 e of thespacer 5 is made deeper.

[0112] Embodiment 7 (FIGS. 1, 2 and 10):

[0113] The passage area is constricted by the spacer 5 to increase theflow speed at the inter-bore portion (FIG. 10) in comparison with otherportions (FIG. 2). The portion with an increased flow speed enjoys anincreased heat transfer rate and therefore an enhanced degree ofcooling.

[0114] In the cylinder block cooling structures of Embodiments 1 to 7,the cylinder bore wall temperature is uniformed in the borecircumferential direction by the spacer 5.

[0115] Cylinder block cooling structures in accordance with Embodiments8 to 12 will be described with reference to FIGS. 11 to 18. As for acylinder block structure, a spacer 5 is formed separately from acylinder block 1, and is disposed within a water jacket 2. In a cylinderblock art related to the invention, the temperature of cooling waterincreases while cooling water introduced via a cooling water inlet flowsaround the high-temperature bore wall. Therefore, although a portion ofthe bore wall near the cooling water inlet is cooled by low-temperaturecooling water, the cooling of the bore wall is insufficient in thevicinity of the cooling water outlet. In embodiments of the invention,the spacer 5 has at least one of structures of Embodiments 8 to 12, soas to serve to uniform the cylinder bore wall temperature in thedirection of cylinder alignment.

[0116] Embodiment 8 (FIGS. 11, 12 and 13A to 13C):

[0117]FIG. 11 shows three boreholes 3 a, 3 b, 3 c disposed in a clyinderblock 1. The cooling water-contact area of the outer peripheral surfaceof the cylinder bore wall is set to a small area near the cooling waterinlet, as shown in FIG. 13A, near cylinder 3 a, and is set to a largearea near the cooling water outlet, as shown in FIG. 13C, near cylinder3 c. FIG. 13B shows the cooling water-contact area of the outerperipheral surface of the cylinder bore wall near cylinder 3 b.

[0118] Embodiment 9 (FIGS. 11, 12 and 14A to 14C):

[0119] The heat transfer rate of the spacer 5 is set to a small valuenear the cooling water inlet, and is set to a great value near thecooling water outlet. The heat transfer rate of the spacer 5 can bereduced by forming an air layer or an oil layer 5 f in the spacer 5 asshown in FIG. 14A, or by forming the spacer 5 from a rubber or an opencell foam rubber and providing a low-heat transfer rate material (e.g.,an isolated cell foam rubber) within the spacer as shown in FIG. 14B.The heat transfer rate of the spacer 5 can be increased by forming thespacer 5 from a rubber or an open cell foam rubber, and providing ahigh-heat transfer rate material (e.g., a metal, a resin, etc.) on aninner surface of the space, as shown in FIG. 14C.

[0120] Embodiment 10 (FIGS. 11, 12 and 15):

[0121] The sectional area of passage of cooling water that contacts theouter peripheral surface of the cylinder bore is made small near thecooling water inlet, as shown in FIG. 15A, and is made large near thecooling water outlet, as shown in FIG. 15B. The cooling water passage atthe cooling water inlet is divided into a plurality of passages, andonly some of the passages are caused to contact the outer peripheralsurface of the cylinder bore. It is desirable that the sum of thesectional areas B and C of the plurality of passages be substantiallyequal to the sectional area A of the cooling water passage at thecooling water outlet, and increases in the flow passage resistance beavoided.

[0122] Embodiment 11 (FIGS. 11, 12, 16 and 17):

[0123]FIG. 16 is a plan view of a cylinder box where the watertemperature at the inlet is 82° C., and the cooling water temperatureincreases while cooling water flows around the bore wall, and thecooling water temperature reaches 90° C. near the outlet. In Embodiment11, the spacer 5 is provided with isolated channels 5 g that leadcooling water to portions of the cylinder bore wall remote from thecooling water inlet, bypassing the water around a portion of thecylinder bore wall near the cooling water inlet, as shown in thehorizontal sectional view of FIG. 17 taken on line XVII-XVII in the planview of the cylinder box structure of FIG. 16. The channels 5 g bring aportion of the cooling water entering via the inlet toward anoutlet-side portion of the cylinder bore wall. For example, a design ismade such that as shown in FIG. 16, if the inlet water temperature is82° C. and the outlet water temperature is 90° C., cooling water havinga water temperature of 82° C. is supplied toward the entire cylinderbore wall via the isolated channels 5 g.

[0124] Embodiment 12 (FIGS. 11, 12 and 18):

[0125] The flow speed around the cylinder bore wall is madeprogressively higher with decreases in the distance to the downstreamend. As for the method for increasing the flow speed, the outlets of theisolated channels 5 g may be constricted progressively toward thedownstream side as shown in FIG. 18. It is also practicable to adoptother means, for example:

[0126] reducing the hole diameter of the head gasket progressivelytoward the downstream side;

[0127] constricting holes of the cylinder head progressively toward thedownstream side;

[0128] disposing an interference plate on a tight plug at a downstreamside to reduce the passage sectional area.

[0129] In a cylinder block cooling structure in accordance withEmbodiments 13 and 14 of the invention, the spacer 5 is formedseparately from the cylinder block 1, and is disposed within the waterjacket 2 as shown in FIGS. 19 and 20. In embodiments of the invention,the spacer 5 has at least one of structures of Embodiments 13 and 14,and serves to uniform the cylinder bore wall temperature in the verticaldirection with respect to the cylinder bores.

[0130] Embodiment 13 (FIG. 19):

[0131] The heat transfer rate of an upper portion of the spacer 5 ismade greater than the heat transfer rate of a lower portion thereof.

[0132] Embodiment 14 (FIG. 20):

[0133] An upper portion of the spacer is provided with a constriction 5h that constricts the gap between the spacer upper portion and the outerperipheral surface of the cylinder bore wall, so that the flow speed isgreater at the upper portion of the spacer than at the lower portionthereof.

[0134] In cylinder block cooling structures in accordance withEmbodiments 15 to 20 of the invention, the spacer 5 is formed separatelyfrom the cylinder block 1, and a structure is provided in which theinserting load on the spacer 5 with respect to the water jacket 2 isreduced or eliminated (reduced-inserting load structure).

[0135] The reduced-inserting load structure has at least one of thestructures of Embodiment 15 to 20.

[0136] Embodiment 15 (FIG. 21):

[0137] Clearances a, a′ are formed between the side surfaces of thespacer 5 and the cylinder block 1 (including the cylinder bore wall 4).

[0138] Embodiment 16:

[0139] The spacer 5 is formed within the water jacket 2. For example, afoam rubber material is charged into the water jacket 2, and is formedinto the spacer 5 by heating.

[0140] Embodiment 17:

[0141] Only a portion of the spacer 5 is provided with a tighteningmargin.

[0142] Embodiment 18:

[0143] A surface treatment for reducing the friction coefficient isperformed on a surface of the spacer 5 that contacts the cylinder block1.

[0144] Embodiment 19 (FIG. 22):

[0145] A structure is provided in which a resin 5 i or the like isapplied onto surfaces of the spacer 5 that contact the cylinder block 1so as to reduce the friction coefficient of the contact surfaces.

[0146] Embodiment 20 (FIG. 23):

[0147] A spacer 5 is formed on a tight plug 8 disposed in a transversehole of the cylinder block 1. Thus, the spacer 5 is provided as atransverse insert type spacer.

[0148] In each one of the cylinder block cooling structures ofEmbodiments 15 to 20, the provision of a reduced-insert load structureallows smooth insertion of the spacer 5 into the water jacket 2.

[0149] In cylinder block cooling structure in accordance withEmbodiments 21 to 29 of the invention, a structure is provided in whichthe spacer 5, formed separately from the cylinder block 1, is preventedfrom lifting up (an uplift preventing structure).

[0150] The uplift preventing structure adopts at least one of thestructures of Embodiments 21 to 29.

[0151] Embodiment 21:

[0152] The spacer 5 is made of a material that has a greater specificgravity than the liquid (water) that flows in the water jacket 2.

[0153] Embodiment 22 (FIGS. 24 and 25):

[0154] Posts 5 j are provided in an upper portion of the spacer 5. Theposts 5 j are pressed from above by the cylinder 9 or the head gasket.

[0155] Embodiment 23 (FIG. 26):

[0156] A head gasket 10 is provided with a protrusion 10 a. Using theprotrusion 10 a, the spacer 5 is pressed from above.

[0157] Embodiment 24 (FIG. 27):

[0158] The cylinder head 9 is provided with a protrusion 9 a. Using theprotrusion 9 a, the spacer 5 is pressed from above.

[0159] Embodiment 25 (FIG. 28):

[0160] A pin 11 is inserted from a side face of the cylinder block 1,thereby retaining the spacer 5.

[0161] Embodiment 26 (FIG. 29):

[0162] A hole 12 is formed in a side surface of the cylinder block 1.The spacer 5 is hooked to the hole 12.

[0163] Embodiment 27 (FIG. 30):

[0164] The spacer 5 is integrated with the cylinder head 9.

[0165] Embodiment 28 (FIG. 31):

[0166] A portion 5 k of the spacer 5 that extends upward is clampedbetween the cylinder head 9 and the cylinder block 1.

[0167] Embodiment 29:

[0168] The spacer 5 is adhered to a water jacket surface.

[0169] In the cylinder block cooling structures of Embodiments 21 to 29,the spacer 5, after being inserted into the water jacket 2, is preventedfrom ascending, due to the provision of an uplift preventing structure.

[0170] In cylinder block cooling structures in accordance withEmbodiments 30 to 38 of the invention, a structure 5 in which thecooling characteristic of the water jacket 2 is set based on at leastone of variation in the bore wall temperature in a directionperpendicular to an axis of a bore 3 and variation in the temperature ofcoolant that flows around the cylinder bore wall 4 is formed by thecylinder block 1 itself, or the spacer 5 provided within the waterjacket 2 formed integrally with the cylinder block 1.

[0171] The structure 5 incorporates at least one of the structures ofEmbodiments 30 to 33, and serves to uniform the cylinder bore walltemperature in the cylinder bore circumferential direction.

[0172] Embodiment 30:

[0173] The wall thickness of the cylinder bore wall 4 is made greater atthe thrust/counterthrust sides than at the inter-bore portion.

[0174] Embodiment 31:

[0175] The cooling water passage is made narrower at thethrust/counterthrust sides than at the inter-bore portion.

[0176] Embodiment 32:

[0177] The heat transfer rate of the spacer at the thrust/counterthrustsides is reduced based on material or structure, in comparison with theheat transfer rate of the spacer at the inter-bore portion.

[0178] Embodiment 33:

[0179] The flow passage is constricted to increase the flow speed at theinter-bore portion.

[0180] The aforementioned structure 5 incorporates at least one of thestructures of Embodiments 34 to 38, and then serves to uniform thecylinder bore wall temperature in the direction of cylinder alignment.

[0181] Embodiment 34:

[0182] The wall thickness of the cylinder bore wall 4 is made greater atthe side of the cooling water outlet 7 than at the side of the coolingwater inlet 6.

[0183] Embodiment 35 (FIGS. 32 and 33):

[0184] The cooling water passage is expanded progressively from the sideof the cooling water inlet 6 to the side of the cooling water outlet 7so that at the thrust/counterthrust sites on the cylinder bore outerperiphery, the area of the cylinder bore wall outer peripheral surfacethat contacts cooling water is increased progressively from the side ofthe cooling water inlet 6 to the side of the cooling water outlet 7.With regard to the spacer 5 formed together with the cylinder block 1,the spacer configuration is reduced progressively from the side of thecooling water inlet 6 to the side of the cooling water outlet 7, at thethrust/counterthrust sites of the cylinder bore outer periphery. SitesA, B, C, D and E in FIGS. 33A-33E correspond to sites A, B, C, D and Ein FIG. 32.

[0185] Embodiment 36:

[0186] A material having a higher heat transfer rate is used for thespacer at the side of the cooling water outlet 7 than at the side of thecooling water inlet 6.

[0187] Embodiment 37:

[0188] The flow passage is constricted to increase the flow speed at theside of the cooling water outlet 7.

[0189] Embodiment 38 (FIG. 34):

[0190] An isolated channel 13 is formed in the cylinder block 1 or inthe spacer 5 formed together with the cylinder block 1 so that theisolated channel 13 conveys cool water toward portions of the cylinderbore wall that are remote from the cooling water inlet 6.

[0191] The structure 5 incorporates at least one of the structures ofEmbodiments 39 to 42, and serves to uniform the cylinder bore walltemperature in the vertical direction relative to each cylinder bore.

[0192] Embodiment 39:

[0193] The wall thickness of the cylinder bore wall is made greater atthe side of a lower portion of each cylinder bore than at the side of anupper portion thereof.

[0194] Embodiment 40:

[0195] The cooling water passage is reduced at the side of a lowerportion of each cylinder bore than at the side of an upper portionthereof.

[0196] Embodiment 41:

[0197] A material with a lower heat transfer rate is used for the spacerat the side of a lower portion of each cylinder bore than at the side ofan upper portion thereof.

[0198] Embodiment 42:

[0199] The cooling water passage located at the side of an upper portionof each cylinder bore is constricted to increase the flow speed at thatlocation.

[0200] Still further embodiments of the invention will be describedbelow with reference to FIGS. 1, 35 and 36,

[0201] In arts related to the invention as shown in FIGS. 61 and 62, thespacer is a single-stage water jacket spacer 33, and the spacer fills alower portion of a water jacket 31. Therefore, a lower portion 32 of thecylinder bore-surrounding portion lacks cooling water, and is likely toexperience insufficient cooling. During a high-load and high-speedoperation of the engine, the temperature of a lower cylinder bore wallportion rises to a high temperature (at least 100° C.) due to slidingfriction heat from the piston rings and the oil rings, thus leading todeteriorated oil consumption (the oil consumption deteriorates due toinsufficient tensions of the piston rings and the oil rings caused bythermal expansion of the inside diameter of the bore walls) andaccelerated degradation of oil (thermal degradation of oil deposited onthe bore wall inner surfaces).

[0202] The aforementioned further embodiments provide cylinder blockcooling structures capable of preventing high temperatures of the lowerportion of the cylinder bore-surrounding portion during the high-loadand high-speed ending operation. In the embodiments, the position ofcooling around each cylinder bore 3 may be changed in accordance withthe state of engine load as indicated in FIG. 35. In particular, whenthe engine load is low, an upper portion 4 a of the cylinderbore-surrounding portion is cooled. When the engine load is high, alower portion 4 b of the cylinder bore-surrounding portion is cooled aswell as the upper portion 4 a thereof. The upper portion 4 a of thecylinder bore-surrounding portion refers to a portion thereof that isabove a midpoint of the piston operation range. The lower portion 4 b ofthe cylinder bore-surrounding portion refers to a portion thereof thatis below the midpoint of the piston operation range.

[0203] The means for cooling the lower portion of the portionsurrounding the cylinder bore 3 during a high-load engine operationunder a condition that the spacer 5 is set is formed by one of thefollowing structures (1) to (5).

[0204] (1) A structure in which the lower portion of the portionsurrounding the cylinder bore 3 is cooled by supplying water to thelower portion of the portion surrounding the cylinder bore 3.

[0205] (2) A structure in which the flow speed of water supplied to thelower portion of the cylinder bore 3-surrounding portion is increased toincrease the degree of cooling.

[0206] (3) A structure in which the rate of heat transfer from the lowerportion of the cylinder bore 3-surrounding portion to the cooling medium(cooling water, a cooling oil, external air) is raised.

[0207] (4) A structure in which the lower portion of the cylinder bore3-surrounding portion is forcibly cooled by delivering air from outsideto a portion of the cylinder block corresponding to the lower portion ofthe cylinder bore 3-surrounding portion.

[0208] (5) A structure in which the lower portion of the cylinder bore3-surrounding portion is forcibly cooled by causing the engine oil toflow around the lower portion of the cylinder bore 3-surrounding portionor by splashing the engine oil to inner surfaces of the cylinder bores.

[0209] In the cylinder block cooling structures of the embodiments ofthe invention, the cooling position in the cylinder bore-surroundingportion is changed in accordance with the state of engine load. Bycooling the lower portion 4 b of the cylinder bore-surrounding portionduring a high-load engine operation, the lower portion 4 b of thecylinder bore-surrounding portion is prevented from having hightemperature during a high-load operation.

[0210] When the engine load is low, only the upper portion 4 a of thecylinder bore-surrounding portion is cooled (the lower portion 4 b ofthe cylinder bore-surrounding portion is not particularly cooled). Whenthe engine load is high, both the upper portion 4 a and the lowerportion 4 b of the cylinder bore-surrounding portion are cooled.Therefore, the lower portion 4 b of the cylinder bore-surroundingportion is prevented from having high temperature when the engine loadis high.

[0211] Constructions and operations that are characteristic ofindividual embodiments of the invention will be described below.

[0212] In the cylinder block cooling structures in accordance withEmbodiments 43 and 44 of the invention as shown in FIGS. 1, 35 and 36,the means for cooling the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation is formedby a means for water-cooling the lower portion 4 b of the cylinderbore-surrounding portion by causing water (engine-cooling water) to flowto the lower portion 4 b of the cylinder bore-surrounding portion.

[0213] The means for cooling the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation has atleast one of the structures of Embodiments 43 and 44.

[0214] Embodiment 43 (FIGS. 1 and 35):

[0215] The cooling water passage provided around a cylinder bore is avertically two-staged cooling water passage. An upper cooling waterpassage 3 a is provided above the spacer 5 in the upper portion 4 a ofthe cylinder bore-surrounding portion. A lower cooling water passage 3 bis provided in the spacer 5 (which may be formed separately from orintegrally with the cylinder block 1) or in the cylinder block 1 in thelower portion 4 b of the cylinder bore-surrounding portion, so as towater-cool the lower portion 4 b of the cylinder bore-surroundingportion. Thus, a means for water-cooling the lower portion 4 b of thecylinder bore-surrounding portion during a high-load engine operation isformed.

[0216] The cooling water passage 2 a in the upper portion 4 a of thecylinder bore-surrounding portion is formed by a passage with a steppedsectional shape which is formed by eliminating an upper portion of thespacer 5 and cutting out an upper inner peripheral portion of the spacer5 (inner peripheral cutout 5 a). A cooling water passage 2 b in thelower portion 4 b of the cylinder bore-surrounding portion is formed byeliminating a portion of the spacer extending from a lower end of thewater jacket 2 to a midpoint of the piston operation range or to aposition below the midpoint, or by reducing the thickness of thatportion of the spacer. The lower portion 4 b of the cylinderbore-surrounding portion is exposed to the cooling water passage 2 b.

[0217] According to this structure, the lower portion 4 b of thecylinder bore-surrounding portion is cooled by engine-cooling waterflowing through the cooling water passage 2 b. Thus, the lower portion 4b of the cylinder bore-surrounding portion is prevented from having hightemperature during a high-load engine operation.

[0218] Embodiment 44 (FIGS. 1 and 36):

[0219] In Embodiment 44, the sectional shape of the cooling waterpassage 2 a in the upper portion 4 a of the cylinder bore-surroundingportion is a rectangular shape with a tapered side which is formed byproviding, as an upper surface of the spacer 5, a slope 5 b thatapproaches the cylinder bore wall 4 as it descends. Other constructionsand operations of this embodiment are the same as or similar to those ofEmbodiment 1.

[0220] In cylinder block cooling structures in accordance withEmbodiments 45 to 48 of the invention, the means for cooling the lowerportion 4 b of the cylinder bore-surrounding portion during a high-loadengine operation is formed by a means for increasing the amount of waterflowing through the lower portion 4 b of the cylinder bore-surroundingportion during a high-load engine operation, as shown in FIG. 1 andFIGS. 37 to 40.

[0221] The means for increasing the amount of water flowing through thelower portion 4 b of the cylinder bore-surrounding portion during ahigh-load engine operation has at least one of the structures ofEmbodiments 45 to 48.

[0222] Embodiment 45 (FIGS. 1, 35, 36 and 37):

[0223] Similar to Embodiments 43 and 44, Embodiment 45 has a verticallytwo-staged cooling water passage arrangement around a cylinder bore. Thesectional shapes of the upper cooling water passage 3 a and the lowercooling water passage 3 b are identical or similar to those inEmbodiments 43 and 44. Embodiment 45 has a means for increasing theamount of water flowing through the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation. The meansfor increasing the amount of water is formed by a valve 15 that isprovided in the cooling water passage 3 b in the lower portion 4 b ofthe cylinder bore-surrounding portion. The valve 15 is capable of beingopened and closed. When the engine load is high, the valve 15 is openedto increase the amount of water flowing through the lower portion 4 b ofthe cylinder bore-surrounding portion. When the engine load is low, thevalve 15 is operated to a reduced opening (not necessarily to acompletely closed state) to stop or reduce the amount of water flowingthrough the lower portion 4 b of the cylinder bore-surrounding portion.

[0224] According to this structure, when the engine load is high, thevalve 15 is opened to increase the amount of engine-cooling waterflowing through the cooling water passage 3 b, so that the lower portion4 b of the cylinder bore-surrounding portion is efficiently cooled.Thus, the structure prevents the lower portion 4 b of the cylinderbore-surrounding portion from having high temperature during a high-loadengine operation.

[0225] Embodiment 46 (FIGS. 1 and 38):

[0226] Embodiment 46 differs from Embodiment 45 in the structure of themeans for increasing the amount of water flowing through the lowerportion 4 b of the cylinder bore-surrounding portion during a high-loadengine operation. That is, the means for increasing the amount of waterflowing through the lower portion 4 b of the cylinder bore-surroundingportion during a high-load engine operation includes a valve body 16capable of opening and closing the cooling water passage 3 b in thelower portion 4 b of the cylinder bore-surrounding portion, and a member17 having an expansion-contraction function, such as a spring or thelike. The amount of contraction of the member 17 is increased so as toincrease the degree of opening of the valve body 16 when the waterpressure on the valve body 16 increases.

[0227] During a high-load and high-speed engine operation, the operationspeed of the water pump is increased to increase the water pressure, sothat the degree of opening of the valve body 16 becomes great.Therefore, the amount of water flowing through the cooling water passage3 b in the lower portion 4 b of the cylinder bore-surrounding portionbecomes great, thereby preventing the lower portion 4 b of the cylinderbore-surrounding portion from having high temperature during a high-loadengine operation. Other constructions and operations of this embodimentare the same as or similar to those of Embodiment 45.

[0228] Embodiment 47 (FIGS. 1 and 39):

[0229] Embodiment 47 differs from Embodiment 45 in the structure of themeans for increasing the amount of water flowing through the lowerportion 4 b of the cylinder bore-surrounding portion during a high-loadengine operation. That is, the means for increasing the amount of waterflowing through the lower portion 4 b of the cylinder bore-surroundingportion during a high-load engine operation is formed by a spacer 5formed from a material (e.g., a sponge) that has an inner peripherycutout 5 a and contracts upon pressure.

[0230] During a high-load and high-speed engine operation, the operationspeed of the water pump is increased to increase the water pressure, sothat the contraction of the spacer 5 becomes great. Therefore, theamount of water flowing through the cooling water passage 3 b in thelower portion 4 b of the cylinder bore-surrounding portion becomesgreat, thereby preventing the lower portion 4 b of the cylinderbore-surrounding portion from having high temperature during a high-loadengine operation. Other constructions and operations of this embodimentare the same as or similar to those of Embodiment 45.

[0231] Embodiment 48 (FIGS. 1 and 40):

[0232] Embodiment 48 differs from Embodiment 45 in the structure of themeans for increasing the amount of water flowing through the lowerportion 4 b of the cylinder bore-surrounding portion during a high-loadengine operation. That is, the means for increasing the amount of waterflowing through the lower portion 4 b of the cylinder bore-surroundingportion during a high-load engine operation is formed by a valve 18 thatis capable of opening and closing the cooling water passage in the lowerportion 4 b of the cylinder bore-surrounding portion and that isprovided at a location other than the spacer 5. When the engine load ishigh, the valve 18 is opened to increase the amount of water flowingthrough the lower portion 4 b of the cylinder bore-surrounding portion.When the engine load is low, the valve 18 is operated to a reducedopening (not necessarily to a completely closed state) to stop or reducethe amount of water flowing through the lower portion 4 b of thecylinder bore-surrounding portion.

[0233] During a high-load and high-speed engine operation, the operationspeed of the water pump is increased to increase the water pressure, sothat the degree of opening of the valve 18 becomes great. Therefore, theamount of water flowing through the cooling water passage 3 b in thelower portion 4 b of the cylinder bore-surrounding portion becomesgreat, thereby preventing the lower portion 4 b of the cylinderbore-surrounding portion from having high temperature during a high-loadengine operation. Other constructions and operations of this embodimentare the same as or similar to those of Embodiment 45.

[0234] In cylinder block cooling structure in accordance withEmbodiments 49 and 50 of the invention, as shown in FIGS. 41 and 42, themeans for cooling the lower portion 4 b of the cylinder bore-surroundingportion during a high-load engine operation is formed by a means forraising the heat transfer rate of the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation and, morespecifically, by a bimetal 19, 20 that includes a material (e.g.,copper) having a higher heat conductivity than the cylinder blockmaterial and that is provided in the lower portion 4 b of the cylinderbore-surrounding portion and that contacts the cylinder bore wall duringa high-load engine operation.

[0235] The bimetal 19, 20 that contacts the cylinder bore wall during ahigh-load engine operation has at least one of the structures ofEmbodiments 49 and 50 described below.

[0236] Embodiment 49 (FIGS. 1 and 41):

[0237] A cooling water passage 3 a is formed in the upper portion 4 a ofthe cylinder bore-surrounding portion. The cooling water passage 3 a isformed by a passage in a stepped sectional shape which is formed byeliminating an upper portion of the spacer 5 and cutting out an innerperipheral portion of the spacer 5, or by a passage in a rectangularsectional shape having a tapered side which is formed by providing as anupper surface of the spacer 5 a slope Sb that descends as it approachesthe cylinder bore wall 4. A lower cooling water passage 3 b is notprovided. A lower portion of the spacer 5 is cut out, and a bimetal 19is provided in the cutout. The bimetal 19 remains off the outerperipheral surface of the cylinder bore wall during a low-load engineoperation. When the engine load becomes high, that is, when the cylinderbore wall temperature becomes high, the bimetal 19 firmly contacts theouter peripheral surface of the cylinder bore wall, so as to transferheat from the cylinder bore wall to the cooling water passage 3 a in theupper portion 4 a of the cylinder bore-surrounding portion by heatconduction, thereby dissipating heat into the cooling water.

[0238] Thus, the lower portion 4 b of the cylinder bore-surroundingportion is prevented from having high temperature during a high-loadengine operation.

[0239] Embodiment 50 (FIGS. 1 and 42):

[0240] In Embodiment 50, a cooling water passage having a sectionalshape that is identical or similar to that in Embodiment 49 is formed inthe upper portion 4 a of the cylinder bore-surrounding portion. A lowercooling water passage 3 b is not provided. A lower portion of the spacer5 is cut out, and a bimetal 20 that also functions as a tight plug isprovided in the cutout in the lower portion of the spacer 5. The bimetal20 remains off the outer peripheral surface of the cylinder bore wallduring a low-load engine operation. When the engine load becomes high,that is, when the cylinder bore wall temperature becomes high, thebimetal 20 firmly contacts the outer peripheral surface of the cylinderbore wall, so as to transfer heat from the cylinder bore wall by heatconduction and thereby dissipate heat into external air.

[0241] Thus, the lower portion 4 b of the cylinder bore-surroundingportion is prevented from having high temperature during a high-loadengine operation.

[0242] Embodiment 51 (FIGS. 1 and 43):

[0243] In the cylinder block cooling structure of Embodiment 51 of theinvention, the means for cooling the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation is formedby a means for air-cooling the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation.

[0244] The means for air-cooling the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation includes anair duct 21 provided outside a cylinder block portion for cooling thecylinder block portion, and an electric fan 22 for delivering air intothe air duct 21. The electric fan 22 is connected to the engine via acoupling in such a manner that the electric fan 22 can be turned on andoff. The revolution speed of the electric fan 22 is linked with theengine revolution speed.

[0245] As for the operation of the means, at the time of a high engineload, the coupling is turned on so that the electric fan 22 operates inaccordance with the engine revolution. Air is thus delivered into theair duct 21, and air is blown from nozzles formed in the air duct 21 toa cylinder block portion of the lower portion 4 b of the cylinderbore-surrounding portion. Thus, the lower portion 4 b of the cylinderbore-surrounding portion is prevented from having high temperatureduring a high-load engine operation.

[0246] In cylinder block cooling structures in accordance with theinvention, means for cooling the lower portion 4 b of the cylinderbore-surrounding portion via an engine oil during a high-load engineoperation has at least one of structures in accordance with Embodiments52 to 54, and cools the lower portion 4 b of the cylinderbore-surrounding portion during a high-load engine operation asindicated in FIGS. 44, 45 and 46.

[0247] Embodiment 52 (FIGS. 1 and 44):

[0248] In Embodiment 52, a cooling water passage 3 a having a sectionalshape that is identical or similar to that in Embodiment 49 is formed inthe upper portion 4 a of the cylinder bore-surrounding portion. A lowercooling water passage 3 b is not provided. In the lower portion 4 b ofthe cylinder bore-surrounding portion, an oil passage 23 that alsofunctions as an oil fall hole passage is formed in the cylinder block 1.The means for cooling the lower portion 4 b of the cylinderbore-surrounding portion via the engine oil during a high-load engineoperation is formed by the oil passage 23.

[0249] According to this structure, during a high-load engine operation,the engine oil from the cylinder head flows down to the oil pan via theoil passage 23, so that the lower portion 4 b of the cylinderbore-surrounding portion is cooled by the engine oil. Thus, the lowerportion 4 b of the cylinder bore-surrounding portion is prevented fromhaving high temperature during a high-load engine operation.

[0250] Embodiment 53 (FIGS. 1 and 45):

[0251] In Embodiment 53, a cooling water passage 3 a having a sectionalshape that is identical or similar to that in Embodiment 49 is formed inthe upper portion 4 a of the cylinder bore-surrounding portion. A lowercooling water passage 3 b is not provided. At the lower cylinder boreportion, a nozzle 25 connected to an oil pump relief valve 24 that isoperated in association with engine revolution is provided. The meansfor cooling the lower portion 4 b of the cylinder bore-surroundingportion via the engine oil during a high-load engine operation includesthe valve 24 and the nozzle 25.

[0252] Therefore, during a high-load engine operation, the oil relievedfrom the oil pump relief valve 24 is ejected from the nozzle 25 and issplashed to the cylinder bore inner surface, so that the lower portion 4b of the cylinder bore-surrounding portion is cooled by the engine oil.

[0253] Embodiment 54 (FIGS. 1 and 46):

[0254] Embodiment 54 differs from Embodiment 53 in the means for coolingthe lower portion 4 b of the cylinder bore-surrounding portion via theengine oil during a high-load engine operation.

[0255] In Embodiment 54, a nozzle 27 is connected to a valve 26 providedin an oil passage in a lower cylinder bore portion. The means forcooling the lower portion 4 b of the cylinder bore-surrounding portionvia the engine oil during a high-load engine operation includes thevalve 26 and the nozzle 27.

[0256] Therefore, during a high-load engine operation, the valve 26 isopened to eject the oil from the nozzle 27. The oil is splashed onto theinner surface of the lower cylinder bore portion, so that the lowerportion 4 b of the cylinder bore-surrounding portion is cooled via theengine oil. Therefore, the lower portion 4 b of the cylinderbore-surrounding portion is prevented from having high temperatureduring an high-load engine operation. Other constructions and operationsof the embodiment are the same as or similar to those of Embodiment 53.

[0257] Still further embodiments of the invention will be described withreference to FIGS. 47 to 70.

[0258] In an art related to the invention in which a cooling water inlet42 (or outlet) is provided in a lower portion of a side portion of acylinder block 41, a spacer 43 is provided substantially closing theinlet 42. In this structure, therefore, cooling water does not easilyenter the cylinder block 41. FIG. 65 shows a plan view of a cylinderblock structure in accordance with a related art. FIG. 66 is a sectiontaken on line VIXVI-VIXVI in FIG. 65. If the spacer 43 is provided witha slit structure 44 as shown in FIGS. 63 to 66, the water passresistance is considerably great and the operation efficiency of thewater pump is low. Furthermore, the flow is likely to become biased, andthe uniformity in cooling deteriorates.

[0259] In an art as shown in FIG. 67 in which a cooling water inlet 42is formed in a cylinder block 41 and therefore cooling water flows intoa water jacket 45 from above, the presence of a spacer 43 reduces thedistance from the inlet 42 to the spacer 43, so that cooling water 46doest not readily flow in. Thus, the flow passage resistance isconsiderably great, and the drive efficiency of the water pump isreduced. Furthermore, as shown in FIG. 68, eddies 47 are formedimmediately downstream of the inlet 42. This unsmoothed flow is likelyto result in biased flow and therefore degrades the cooling uniformity.

[0260]FIG. 69 shows a plan view of a related-art cylinder blockstructure. FIG. 70 shows a section taken on line VIIX-VIIX in FIG. 69.As for cooling water outlets 48, as shown in FIGS. 69 and 70, streams ofcooling water flowing along two sides of the line of cylinder bores forma confluent portion 40. In the confluent portion 40, streams collide,forming a stagnation portion 49. Due to this unsmoothed flow, the waterpass resistance is great, and the drive efficiency of the water pump isreduced.

[0261] As yet further embodiments of the invention, cylinder blockcooling structures capable of reducing the water pass resistance andimproving the cooling uniformity are provided. As shown in FIGS. 47 to51, it is practicable to adopt a structure in which a spacer portion 5 adisposed at a cooling water inlet portion 6 or a cooling water outletportion 7 in the cylinder block 1 achieves a reduced flow resistance incomparison with the related-art structures shown in FIGS. 63 to 70. Dueto the structure in accordance with embodiments, the flow resistancerelated to the inflow and outflow of cooling water with respect to thewater jacket 2 formed in the cylinder block is reduced, so that thedrive efficiency of the water pump rises and the fuel economy improves.Furthermore, the inflow and outflow of cooling water with respect to thewater jacket 2 becomes smooth and stable, thereby achieving good effecton the cooling uniformity regarding the cylinder bore wall 4.

[0262]FIG. 50 shows a plan view of a cylinder block cooling structure inaccordance with Embodiments 55 to 57 of the invention. FIG. 51 shows asection that includes a section taken on line VXI-VXI in FIG. 50. In thecylinder block cooling structures of Embodiments 55 to 57, a spacerportion 5 a is disposed in the cooling water inlet portion 6 in a sideportion of the cylinder block 1 as shown in FIGS. 47 to 51. Theaforementioned flow resistance-reducing structure is formed by astructure in which a passage that does not cause a greater passageresistance than the conventional structures shown in FIGS. 63 to 70.More specifically, the flow resistance-reducing structure has at leastone of the structures of Embodiments 55 to 57 described below.

[0263] Embodiment 55 (FIG. 47):

[0264] A portion corresponding to a cooling water inlet 6 a is providedwithout a spacer.

[0265] Embodiment 56 (FIG. 48):

[0266] The thickness of the spacer 5 is made less in a portioncorresponding to the cooling water inlet 6 a than in the other portionsof the spacer 5.

[0267] Embodiment 57 (FIGS. 49 to 51):

[0268] The spacer 5 is provided with a slope 28 or a curved surface fordirecting the flow diagonally upward, along an outer peripheral surfaceof the cylinder bore wall 4 from a portion facing the cooling waterinlet 6 a.

[0269] In the structures of Embodiments 55 and 56, the passage sectionalarea is expanded to reduce the water pass resistance. In the structureof Embodiment 57, the spacer 5 is provided with the slope 28 or thecurved surface, thereby reducing the water pass resistance.

[0270] In cylinder block cooling structures in accordance withEmbodiments 58 to 60 of the invention, a spacer portion 5 a is disposedin a cooling water inlet portion 6 in an upper portion of the cylinderblock 1 as shown in FIGS. 52 to 54. The flow resistance-reducingstructure has at least one of the structures of Embodiments 58 to 60described below.

[0271] Embodiment 58 (FIG. 53):

[0272] A portion corresponding to a cooling water inlet 6 a is providedwithout a spacer.

[0273] Embodiment 59 (FIG. 54):

[0274] The spacer 5 is made thinner in a portion thereof extending froma portion facing a cooling water inlet 6 a along the outer surface ofthe cylinder bore wall 4.

[0275] Embodiment 60 (FIGS. 55 and 56):

[0276] A portion of the spacer 5 extending from a portion facing thecooling water inlet 6 a along the outer surface of the cylinder borewall 4 is provided with a slope 29 or a curved surface for directing theflow diagonally upward.

[0277] In the structures of Embodiments 58 and 59, the passage sectionalarea is expanded to reduce the water pass resistance. In the structureof Embodiment 60, the spacer 5 is provided with the slope 29 or thecurved surface, thereby reducing the passage resistance.

[0278] In cylinder block cooling structures in accordance withEmbodiments 61, 62 of the invention, a spacer portion 5 b is formed by aweir 5 b disposed at a cooling water outlet portion 7 in an upperportion of the cylinder block 1. The flow resistance-reducing structureis formed by a structure in which no confluent portion exists in acooling liquid passage, or a structure in which stagnation is reducedeven though there is a confluent portion. More specifically, the flowresistance-reducing structure is formed by slopes 30 or curved surfacesthat are formed on both sides of the weir 5 b so as to turn the flowcoming via both sides of the cylinder bore alignment into an upward ordiagonally upward flow.

[0279] The weir 5 b is formed as in Embodiment 61 or 62. FIGS. 57 and 59show plan views of cylinder blocks. FIGS. 58 and 60 show a section takenon line VXVIII-VXVIII in FIG. 57 and a section taken on line VIX-VIX inFIG. 59, respectively.

[0280] Embodiment 61 (FIGS. 57 and 58):

[0281] A weir 5 b is formed in a spacer 5 that is formed separately fromthe cylinder block 1.

[0282] Embodiment 62 (FIGS. 59 and 60):

[0283] A weir 5 b is formed in a spacer 5 that is formed integrally withthe cylinder block 1.

[0284] In a case where the weir 5 b is formed integrally with thecylinder block 1, the casting mold structure becomes complicated, andthe bore deformation deteriorates due to the bolt tightening force atthe time of fastening the cylinder head. Therefore, it is desirable thatthe weir 5 b be formed separately from the cylinder block 1.

[0285] In the structures of Embodiments 61 and 62, the weir 5 beliminates a confluent portion where streams coming via two sides of thecylinder bore arrangement meet and collide. Furthermore, the slopes 30or curved surfaces formed on the weir 5 b make smooth flow toward theoutlet.

[0286] In Embodiments 55 to 62, the cooling water inflow resistance oroutflow resistance with respect to the water jacket in the cylinderblock is reduced. Therefore, the drive efficiency of the water pumprises, and the fuel economy improves. The inflow or outflow of coolingwater with respect to the water jacket 2 becomes smooth and stable.Therefore, biased flow in the water jacket 2 in the cylinder blockbecomes less likely, and good effect is provided on the coolinguniformity with regard to the cylinder bore wall 4.

[0287] While the present invention has been described with reference towhat are presently considered to be preferred embodiments thereof, it isto be understood that the present invention is not limited to thedisclosed embodiments or constructions. On the contrary, the presentinvention is intended to cover various modifications and equivalentarrangements.

What is claimed is:
 1. A cooling structure of a cylinder block, comprising: a water jacket continuously extending around a cylinder bore wall so as to convey a cooling medium, the cooling medium cooling the bore wall by flowing around the bore wall; and a mechanism that sets a cooling characteristic of the water jacket based on at least one of a variation in a temperature of a cylinder bore wall in a direction perpendicular to an axis of boreholes and a variation in a temperature of the cooling medium in the direction perpendicular to the axis of boreholes, passing around the bore wall.
 2. A cooling structure according to claim 1, wherein the mechanism includes a spacer disposed in the water jacket.
 3. A cooling structure according to claim 2, wherein the spacer has a structure in which a cooling capability with respect to an inter-cylinder bore wall portion is higher than a cooling capability with respect to a different site.
 4. A cooling structure according to claim 3, wherein the cooling capability of the spacer with respect to the inter-cylinder bore wall portion is made higher than the cooling capability of the spacer with respect to a thrust/counterthrust side of the cylinder bore wall.
 5. A cooling structure according to claim 3, wherein a heat transfer rate of the spacer at a thrust/counterthrust side of the cylinder bore wall is made lower than a heat transfer rate of the spacer at the inter-cylinder bore wall portion.
 6. A cooling structure according to claim 3, wherein a heat transfer rate of the spacer at the inter-cylinder bore wall portion is made higher than a heat transfer rate of the spacer at a thrust/counterthrust side of the cylinder bore wall.
 7. A cooling structure according to claim 2, wherein the spacer has a structure in which a cooling capability with respect to an outer periphery of the cylinder bore wall disposed downstream in a cooling water passage is made higher than a cooling capability with respect to an outer periphery of the cylinder bore wall disposed upstream of the cooling water passage.
 8. A cooling structure according to claim 2, wherein the spacer has a structure in which a cooling capability with respect to an upper portion of a cylinder bore wall outer periphery is made higher than a cooling capability with respect to a lower portion of the cylinder bore wall outer periphery.
 9. A cooling structure according to claim 2, wherein the spacer has a structure in which a load for inserting the spacer into the water jacket is reduced or eliminated.
 10. A cooling structure according to claim 2, wherein the spacer has a structure in which the spacer is prevented from ascending in the water jacket.
 11. A cooling structure according to claim 2, wherein the spacer has a structure for reducing a flow resistance, in a portion of the spacer disposed in a cooling water inlet portion or a cooling water outlet portion of the cylinder block.
 12. A cooling structure according to claim 11, wherein the portion of the spacer is disposed in the cooling water inlet portion in a side portion of the cylinder block or in the cooling water inlet portion in an upper portion of the cylinder block, and wherein a thickness of a portion corresponding to the cooling water inlet portion is less than in the other portions of the spacer.
 13. A cooling structure according to claim 11, wherein the portion of the spacer is formed by a weir disposed in the cooling water inlet portion in an upper portion of the cylinder block, and the structure for reducing the flow resistance includes a slope or a curved surface that is formed on each one of right and left side surfaces of the weir so as to turn a flow coming along two opposite sides of the cylinder bore into an upward or diagonally upward flow.
 14. A cooling structure according to claim 2, wherein the spacer is formed separately from the cylinder block.
 15. A cooling structure of a cylinder block, comprising: a water jacket continuously extending around a cylinder bore wall so as to convey a cooling medium, the cooling medium cooling the bore wall by flowing around the bore wall; a spacer disposed in the water jacket; and a mechanism that changes a position of cooling around an outer wall of the bore in accordance with a state of engine load.
 16. A cooling structure according to claim 15, wherein when the engine load is low, the mechanism cools an upper portion of a cylinder bore-surrounding portion, and wherein when the engine load is high, the mechanism cools the upper portion of the cylinder bore-surrounding portion and a lower portion of the cylinder bore-surrounding portion.
 17. A cooling structure according to claim 16, wherein the mechanism comprises at least a cooling water passage formed in the spacer positioned in the lower portion of the cylinder bore-surrounding portion, and the mechanism cools the lower portion of the cylinder bore-surrounding portion via a water.
 18. A cooling structure according to claim 17, wherein the mechanism comprises a water amount controller that increases an amount of water in the cooling water passage of the spacer disposed in the lower portion of the cylinder bore-surrounding portion when the engine load is high.
 19. A cooling structure according to claim 16, wherein the mechanism comprises a bimetal that is provided in the lower portion of the cylinder bore-surrounding portion so as to contact the cylinder bore wall when the engine load is high, and the bimetal includes a material that has a higher heat conductivity than a material of the cylinder block.
 20. A cooling structure according to claim 16, wherein the mechanism comprises an air duct that is provided outside a cylinder block portion present in the lower portion of the cylinder bore-surrounding portion so as to cool the cylinder block portion, and the mechanism cools the cylinder block portion via an air when the engine load is high.
 21. A cooling structure according to claim 16, wherein the mechanism comprises an engine oil passage in the lower portion of the cylinder bore-surrounding portion or comprises a nozzle for splashing an engine oil to an inner surface of the cylinder bore, and wherein when the engine load is high, the mechanism cools the lower portion of the cylinder bore-surrounding portion via the engine oil by passing the engine oil through the engine oil passage or ejecting the engine oil from the nozzle.
 22. A cooling structure according to claim 15, wherein the spacer has a structure for reducing a flow resistance, in a portion of the spacer disposed in a cooling water inlet portion or a cooling water outlet portion of the cylinder block.
 23. A cooling structure according to claim 22, wherein the portion of the spacer is disposed in the cooling water inlet portion in a side portion of the cylinder block or in the cooling water inlet portion in an upper portion of the cylinder block, and wherein a thickness of a portion corresponding to the cooling water inlet portion is less than in the other portions of the spacer.
 24. A cooling structure according to claim 22, wherein the portion of the spacer is formed by a weir disposed in the cooling water outlet portion in an upper portion of the cylinder block, and the structure for reducing the flow resistance includes a slope or a curved surface that is formed on each one of right and left side surfaces of the weir so as to turn a flow coming along two opposite sides of the cylinder bore into an upward or diagonally upward flow.
 25. A cooling structure according to claim 15, wherein the spacer is formed separately from the cylinder block. 